In typical electronic networks, particularly those composed of a number of interconnected bus agents (e.g., semiconductor devices) within a computer system, some of the physical interconnective pathways may be driven to a constant value for the duration or some other period of operation of the network. Within an electronic network, such as a computer system, this means that certain bus traces that connect bus agents within the computer system may be driven to a static value, such as a logical “1”, “0”, or an indeterminate value, such as “tri-state”.
Driving a particular bus trace to a value typically requires the input/output (“I/O”) of one of the bus agents connected to the bus trace to force the value onto the bus trace, thereby using power for the duration of the operation of the computer system. Similarly, an I/O of the receiving agent may also consume power while the transmitting agent is driving a constant value. The term “drive” when used in the context of a value placed on a bus, can also refer to the static power drawn when no current is flowing in the bus or corresponding I/O. Alternatively, the bus trace may be connected to a circuit that holds the device at a certain state without requiring a device I/O to drive the bus trace to that value. However, in this configuration the circuit that drives the bus trace to a particular value may consume current and therefore contribute to the power consumption of the computer system.
FIG. 1 is a prior art example of a portion of a computer system in which a bus trace connecting two bus agents drives a constant value onto the bus trace in order to represent a static value. In some prior art applications, the driver may consist of an inverter circuit, for example, that draws power due to leakage currents within the semiconductor devices of which the circuit is composed.
In a typical point-to-point (PtP) computer system in which a common system interface (CSI) bus architecture and protocol is used, each link between the bus agents may contain numerous traces or “lanes” that are used to transmit data from a transmitting agent to a receiving agent. Regardless of whether the lanes are operating in a dynamic, or “switching” mode, or a static mode, in which a constant value is driven onto the lane, power may be drawn by the lane due to, for example, leakage or other sources within the input/output (“I/O”) circuits within the receiving and/or transmitting agents.